1. FIELD OF THE INVENTION:
This invention relates to monitoring devices and more particularly relates to monitoring devices used to detect malfunctioning fluid dispensers.
1. STATEMENT OF ART:
Typical fluid dispensing systems in one form include a pump having an inlet connected to a supply of material and a discharge connected to a dispenser. For precision dispensing, the dispenser may include a valve which permits fluid to pass through a discharge opening such as a nozzle or fluid tip. In some systems the dispenser valve is operated by a programmed control device so that fluid is dispensed in precise or metered amounts.
In many applications it is often desirable that precise patterns, metered amounts or both be dispensed. In operation, precision or accurate metering is affected by many factors including nozzle wear, fluid impurities, nozzle clogging, and pump performance.
Clogging of the material flow path, especially in the dispenser, is a typical problem that adversely affects the performance of precision dispensing systems. For example, in precision dispensing systems used to coat the interior surface of multipiece can bodies, a clogged or worn nozzle may cause the can body to be incompletely or improperly coated.
The can bodies are typically coated during the process of manufacture at rates of up to many hundreds of cans per minute. Thus, an improperly functioning dispenser and more particularly a clogged or worn nozzle can result in many improperly coated cans before detection by inspection or other known means. An improperly coated can may have an adverse effect on the can's ability to function for storage. In some cases, the can may suffer accelerated deterioration (i.e., shortened shelf life), and in others (e.g. for foods and beverages) the contents may be adversely affected (e.g., taste, spoilage). Improper coating, therefore, is undesirable and may also be costly because cans that are improperly coated typically are not usable.
Other systems, for example, those involving the precise deposition of thermoplastics or similar materials, are also susceptible to clogging. An example of such a system is described in U.S. Pat. No. 4,166,246--Matt. These systems are typically used in the manufacturing of packaging (e.g., cardboard cartons) and in product assembly. Clogging of the dispensing system may result in defective products and in turn result in delays or otherwise introduce undesirable additional costs in the manufacturing process.
Clog sensing systems heretofore known are not applicable or useful for the accurate and prompt clog sensing desired. For example, U.S. Pat. No. 4,072,934--Hiller, et al., discloses a method and apparatus for detecting blockages in a vapor flow line such as those used in liquid gasoline dispensing systems. Such an apparatus would not be useful in a precision coatings application because the nozzle condition, whether clogged or worn, cannot be determined. Hiller et al. determines whether a blockage exists in a vapor line by sensing the pressure on either side of the clog and activating an alarm when the differential pressure exceeds a predetermined maximum value.
U.S. Pat. No. 3,816,025--O'Neill describes a fluid circulation system for a paint spray installation. A secondary recirculation loop pressure sensor senses the pressure in the secondary loop dropping below a preselected value in order to shut down the paint supply pump if a paint flow line should break.
U.S. Pat. No. 4,315,317--Orchard et al. discloses a measuring, computing and recording system for monitoring of spray application parameters for pesticides dispensed from an aircraft. Orchard et al. records pressure information, total liquid volume, liquid flow rate, spray passes and spray time. The user is required to interpret the results of the items recorded to determine whether among other things a clog condition is present. Such a delay in system condition determination is wholly unacceptable for precision coating applications such as the can body example illustrated above.
U.S. Pat. No. 3,482,781--Sharpe contains a paint spray gun which uses air to atomize the paint during dispensing. A pressure gauge is affixed to the gun to indicate the pressure of the atomizing air during dispensing operation. This device cannot accurately and reliably determine whether the paint flow path is clogged.
There is no system presently known which quickly and automatically determines whether a dispenser is applying a coating material in other than a preselected or desired fashion.